1. Field of the Invention
The present invention relates to an electro-mechanical clutch actuator, and more particularly, to an algorithm for an electro-mechanical clutch actuator for automated shifting of a manual transmission.
2. Background and Summary of the Invention
Both manual and automatic-shift transmissions are well known in the automotive industry. Manual transmissions typically include a shift lever which is manually operated by a vehicle operator to shift the manual transmission between the various gear ratios which are provided. In such a system, the shift lever is connected with a linkage system which is utilized to selectively engage a selected gear of an input shaft/counter-shaft manual transmission system. During the disengagement of one gear ratio and the subsequent engagement of another gear ratio, a clutch is typically disengaged in order to release the transmission input shaft from driving engagement with the engine output shaft. This clutch is typically disengaged by a clutch cable or rod which is connected to a foot pedal which is depressed by the vehicle operator prior to shifting gears and subsequently released upon completion of a gear shift operation.
During the operation of a vehicle having a manual transmission, a vehicle operator can become accustomed to the rate at which the clutch pedal can be depressed and released for disengaging and reengaging the clutch for smooth operation of the vehicle during shifting operations.
As a clutch disk wears down over its useful life, the clutch pedal position at which the clutch disk/clutch cover assembly begins to transmit significant torque changes with respect to the driver's position within the vehicle. In addition, the clutch cover/clutch disk assembly may exhibit different rates of clutch apply for the same rate of clutch pedal motion by the driver dependent upon the geometry of the linkage that connects the clutch pedal to the clutch disk/cover assembly. Also, the clutch cable or rod often needs to be manually adjusted as the clutch disk wears down in order to provide proper disengagement and reengagement of the clutch.
Manual transmissions are widely considered to be more efficient than automatic transmissions since automatic transmissions have large parasitic losses associated with the pressurized hydraulic fluid systems which must be maintained for pressurizing the torque converter and hydraulically engaging and disengaging each of the clutch packs and brake assemblies which are typically associated with an automatic transmission. However, despite the relative inefficiency of an automatic transmission relative to a manual transmission, the simplicity and convenience of driving a vehicle having an automatic transmission is still preferred by a large portion of the automobile consumers.
Accordingly, the present invention is directed toward providing automated shifting of a manual transmission in order to provide a vehicle with a transmission which has the simplicity and convenience of an automatically shifted transmission but which does not have the parasitic losses associated with a standard automatic transmission, in particular, those associated with a torque converter and a hydraulic actuator system.
In providing automated shifting of a manual transmission, the electro-mechanical clutch actuator of the present invention is provided for disengaging and engaging the clutch of a manual-type transmission. The electro-mechanical clutch actuator is provided with an assist spring/cam assembly which is designed to reduce the load on the electric motor such that the load-compensating assist spring counteracts the clutch cover spring leaving only the frictional and inertial forces of clutch cover motion to be supplied by the electric motor. Additionally, the load-compensating assist spring allows the shift (including clutch release and engagement) to be made faster and with a reduced-size motor. The clutch actuator also includes a mechanical wear adjuster which automatically adjusts the position of the release linkage as a clutch disk wears over its useful life.